Chronic Wasting Disease (CWD)

Chronic wasting disease (CWD) is a fatal neurodegenerative prion disease that affects cervid species, including deer, elk, moose, and caribou. It is a transmissible spongiform encephalopathy (TSE) that was discovered in the late 1960s. Since then, the disease has expanded both geographically and in terms of the species it affects. The distinguishing feature of CWD is its ease of transmission, which sets it apart from other prion diseases. This easily transmissible phenomenon has resulted in growing public health concerns for deer populations and humans. BioVenic has dedicated considerable attention to studying the pathogenesis and transmission dynamics of CWD for many years to help animal health researchers mitigate the adverse effects of the disease.

Cause

CWD is caused by abnormal prion proteins that can induce misfolding of normal prion proteins in a self-propagating manner. The exact origin of these prions is still under investigation, but it is suspected that they may arise through spontaneous mutation or from an external source, such as contaminated environments or infected animals. The misfolded prions accumulate in the central nervous system, causing physical degeneration, lack of coordination, dramatic changes in behavior, and long-term physical exertion until death.

Fig. 1 Schematic representation of hypothetical origins of CWD.¹

Geographic Distribution

The initial detection of the disease traces back to 1967 at the Southern Colorado Wildlife Research Facility, where a mule deer exhibited signs of wasting syndrome. However, it wasn't until 1978 that it was recognized as a disseminated spongiform encephalopathy. Subsequently, in 1981, the presence of the disease was confirmed in wild deer populations in Colorado, while in 1996, its occurrence was established in artificial breeding farms. US, Canada, Norway, Finland, Sweden, and South Korea have all reported CWD breaks. Currently, CWD has been detected in 29 US states, and the disease continues to spread.

Main Impacts

• Among all TSE diseases, only CWD and sheep scrapie can be transmitted laterally to sensitive hosts through infected animals or infection source reservoirs, so CWD is likely to expand its geographical distribution.
• CWD is probably the most efficiently transmitted of all the prion diseases. In dense free-ranging herds, prevalence can reach 40%, and in captive herds, 100%.
• CWD affects both captive and free-ranging animals, necessitating significant and intricate efforts for monitoring, control, or eradication.

Transmission

CWD can be spread through direct contact with bodily fluids including saliva, blood, feces, and urine, as well as indirectly through environmental contamination. Infected animals shed prions into their surroundings, thereby contaminating soil, vegetation, and water sources. The disease can spread horizontally within populations and vertically from infected mothers to offspring. Although there is currently limited evidence of transmission to humans, there are concerns about the potential for chronic disease transmission.

Fig. 2 Animal species that CWD may infect.¹

Signs and Symptoms

CWD has an average incubation period of around 22 months and predominantly affects adult animals in the age range of 3 to 5 years old. The disease is characterized by progressive weight loss and behavioral changes, including abnormal behavior, depression, drooping head, excessive salivation, increased thirst, frequent urination, expressionless face, and pacing within the enclosure. In the case of elk, symptoms may manifest as hyperactivity and nervousness. Although the animals are addicted to grains, they lack interest in forage, gradually lose weight, become weak and finally die.

Diagnosis of CWD

Laboratory diagnosis is an effective way to confirm the diagnosis of CWD. BioVenic helps customers develop precise diagnostics solutions based on immunodiagnostics and protein in vitro amplification technologies to detect abnormal prion proteins in brain tissue, lymphoid tissue, and neuroendocrine tissue, including,

• Immunohistochemistry (IHC)
• Western blotting (WB)
• ELISA
• Prion misfolding cyclic amplification (PMCA)
• Real-time quaking-induced conversion (RT-QuIC)

Among them, IHC is considered the gold standard for diagnosing CWD.

Treatment

Currently, there are no known treatments or cures for CWD. Once an animal is infected, the CWD progresses relentlessly, leading to death. Research efforts are ongoing to explore potential therapeutic interventions, but no effective treatment has been identified.

Prevention and Control

Together with government agencies and research institutions, BioVenic develops and promotes best practices for preventing and controlling CWD. We recommend the following measures:

• Preventive Measures
  Quarantine measures should be implemented in non-CWD-infested areas to prevent the introduction of CWD through deer animals, restrict the movement of deer animals, and carry out population management. Potentially infected animals should be culled immediately and their carcasses buried or incinerated.
• Management Techniques to Control CWD
  Create a network to monitor and track the spread, frequency, and geographic distribution of the disease outbreak. In limited geographic areas, captive or free-ranging herds may be reduced. Treatments and vaccines may be future options, but none of these tools are currently available.
• Comprehensive Management
  The government can compensate farmers for slaughter losses in the removal of CWD. The farming of cervids should be prohibited in areas where CWD is outbreaking.

CWD is undoubtedly a major problem for wildlife populations. BioVenic provides customers with diagnostic development services that enable early detection. To curb the spread of CWD and protect animals, we also help customers develop vaccines, formulate protective measures, etc. If you need our help, please contact us today.

Reference

1. Pritzkow, Sandra. "Transmission, strain diversity, and zoonotic potential of chronic wasting disease." Viruses 14.7 (2022): 1390.